@Julie
Will that prevent long lines?
If you get tickets on line on the above posted official sites, there is no reason to wait in line to buy the tickets. Nobody skips the security line.
@Peter
Uffizi. Peter, I assume you have reached this page: https://i.postimg.cc/65D9JG0L/uffizi.jpg
Did you check the privacy box (1), before clicking the "continue" button (2)?
Vatican Museums Did you use the official site posted above? Are you 101% sure that the transaction wasn't blocked by the Verified-by-Visa safety protocol? Did you check the spam folder?
Yes, yes and yes? It seems you don't need any voucher to enter, as long as you know the day and time you are supposed to be there.